1. Technical Field
The present invention relates to a manufacturing method of a semiconductor device. More specifically, the present invention relates to a dicing technique of a semiconductor device having a metal support by using a laser scribing method.
2. Related Art
Owing to the technological progress of recent years, optical semiconductor devices, such as a light emitting diode, have achieved a higher efficiency and higher output powers. However, along the increase in the output power, the amount of heat generated by the optical semiconductor device has increased, which has caused a problem of reliability degradation such as efficiency degradation of an optical semiconductor device and deterioration of a semiconductor film. In order to solve these problems, the growth substrate that typically has a relatively low thermal conductance has been discarded and replaced with a structure in which a metal support having a relatively high thermal conductance is provided to support semiconductor films (Patent Document 1). With the support structure described above, heat dissipation of an optical semiconductor device is improved and in addition, due to the removal of the growth substrate, the light emitting efficiency, specifically the light extracting efficiency, is improved. More specifically, it becomes possible to reduce absorption of light passing through the growth substrate as well as reduce a component of the light that is totally reflected at an interface between the semiconductor film and the growth substrate due to the difference in their respective refractive indices.
When a metal is used to support a semiconductor film in place of the growth substrate, it is common to use a laser scribing method in order to dice semiconductor devices that include the metal support in a wafer state into individual chips. In a laser scribing method, a laser beam is radiated along dividing lines of a wafer so that the energy of the leaser beam forms dividing grooves by heating and melting or evaporating the material, thereby separating the wafer into individual semiconductor chips. The reason why such a method is used is because it is difficult to divide a wafer stably by using other methods and the difficulty of the dividing affects the yield. For example, in a dicing method, due to the ductibility of the metal which constitutes the support, clogging of a dicing blade often occurs, and a blade needs to be replaced a number of times during the dicing process of the semiconductor device, which leads to a decrease of the work efficiency and an increase in the production cost. On the other hand, in a scribing/breaking method, there is a problem in that the wafer is only bent due to the ductibility of the metal, and a wafer cannot be divided. In these dicing method and scribing/breaking method, the thicker the metal support is, the more significant the above mentioned problem becomes.    [Patent Document 1] Japanese Laid-Open Patent Application Publication No. 2007-536725.
However, even when a semiconductor device having a metal support is separated by using the laser scribing method, there have been the following problems.
In a semiconductor device having a metal support, before cutting a metal support by a laser scribing method, grid-like grooves (called as “street grooves” hereinafter) are formed in a semiconductor film along the dividing lines of semiconductor devices so as to partition semiconductor devices into rectangular compartments. As a result, the metal support is exposed at the bottom of the street grooves. Then, a laser beam is radiated onto the metal support that is exposed along the street groves, and dividing grooves are thereby formed by melting or evaporating the metal support using the energy of the laser beam. This should complete the device separation. However, the device separation may not properly occur, if a molten metal caused by the irradiation of the laser is not completely removed and remains inside the dividing groove, causing welding of the metal support again in the dividing groove. FIG. 1 is a cross-sectional photograph of a metal support in which a dividing groove is formed by using a conventional laser scribing method. As shown in the figure, when a semiconductor device has a thick metal support or when a low power laser is used, the molten metal may weld the metal support again inside the dividing groove, resulting in an incomplete device separation. In such a situation, due to the ductibility of a metal, trying to break the wafer leads to bending of the wafer and not to a proper separation of semiconductor devices, or results in diced semiconductor devices that have metal burrs on their sides, which causes a difficulty in insuring a high yield.
In order to avoid these improper separations, a higher power laser output is required. However, when a high power laser is radiated onto the metal support, metal particles fly apart from the metal support, and are attached on the side face of the semiconductor film, causing current leakage and/or short circuit, which are undesirable. In order to solve the problem of the metal attachment, the width of the street grooves needs to be widened so that the spacing between neighboring semiconductor devices is enlarged. However, increasing the width of the street grooves would result in increased production costs, because the number of semiconductor devices that can be made out of a single wafer (in other words, the “chip yield” of semiconductor devices) would be reduced. As described above, for semiconductor devices having a metal support, it has been difficult to achieve proper separation of semiconductor devices while ensuring appropriate levels of the production yield and the chip yield.
Because of the fact that the thicker a metal support is, the more significant the above mentioned problems become, from the point of view of insuring the production yield rate and the chip yield in the conventional manufacturing method, the thickness of the metal support has been considered to be limited to about 60 μm or less. On the other hand, considering heat dissipation performance and handling ability (the ease of mounting to each device and transportation) of semiconductor devices, it is desirable that the thickness of a metal support film be increased. Therefore, it has been desired to have a manufacturing method by which semiconductor devices having a metal support of 60 μm or larger in thickness can be stably manufactured.